The present invention generally relates to inkjet printing systems, and more particularly to an inkjet printing system having a printhead servicing station that is automatically actuated by movement of the printhead carriage.
The field of electronic printing has seen significant advancements made in recent years. Specifically, the technology has developed to the point where a wide variety of highly efficient printing systems are available which are capable of dispensing ink in a rapid and accurate manner. In particular, thermal and piezoelectric inkjet systems have become highly reliable and produce an excellent image. Thermal inkjet printers basically include an ink reservoir in fluid communication with a substrate having a plurality of resistors thereon. Selective activation of the resistors causes thermal excitation of the ink and expulsion thereof through nozzles of the printhead. Piezoelectric inkjet printers utilize individual piezoelectric electric elements instead of resistors. The piezoelectric elements are also selectively excited resulting in a corresponding excitation of the ink and expulsion thereof through the nozzles.
In general, in either type of inkjet printing system, an important component of the printhead is an orifice plate having a plurality of openings therein. Each opening is associated with a corresponding resistor or piezoelectric element. Upon excitation of the resistor or piezoelectric element, the ink is ejected through these openings and onto the item being printed on. Thus, the openings are in effect nozzles which emit ink. In order to ensure proper operation of the inkjet printing system, the orifice plate and openings must be kept free and clean of debris at all times. If they are not, a number of problems can occur which will impair the performance of the printer. For example, if debris such as stray paper fibers collect on the orifice plate they can reduce the quality of the formed image, cause smearing of the image, and block or interfere with expulsion of the ink through the openings in the orifice plate. Moreover, if ink is permitted to dry on the orifice plate or within the openings, the same types of problems can occur.
In order to overcome the above-mentioned problems, devices known as "service stations" have been developed. These service stations are typically positioned so that when the printhead is not in use, it is "parked" over the service station. Typical service stations can have a variety of components, but some typical maintenance functions include: a) sealing the printhead with a hermetic cap during idle time to prevent the nozzles from clogging due to ink drying over or inside of the nozzles, b) periodic wiping of the orifice plate and openings to remove dust, debris, and excess ink, c) providing an area where the printhead can spray or "purge" itself to clean the nozzles, and d) providing a controlled vacuum burst to the nozzles to clear out a clogged nozzle.
The above-mentioned service stations have primarily been designed in connection with printing devices such as typewriters and independent printers used in connection with personal computers. While the need to ensure that the printhead nozzles remain clean is important in these types of applications, it is not as critical as where inkjet printers are used in mail handling machines. Because of the ability to readily change the image printed by an inkjet printer simply through software changes, the use of inkjet printers in mailing machines is a considerable improvement over prior art rotary printing drums or conventional flat printing platens. However, the quality of the printing of postage indicia including, for example, postage value, city of origin, and zip code, is tightly controlled by the postal authorities of individual countries to deter fraudulent printing and to permit the easy reading of the indicia by postal authority automated reading equipment. Thus, in this type of environment the need to ensure the cleanliness of the printhead nozzles becomes very critical. Further compounding the problem of cleanliness is the fact that mail handling machines present a much harsher environment than the printing mechanisms previously discussed. Since high volume mail handling machines process very large numbers of mailpieces at very high speeds, the amount of paper dust created can be very significant thereby further complicating the design of an effective service station. Thus, there is a need for a service station for an inkjet printing system used in a mail handling machine which is simple in operation and which assuredly cleans the printhead nozzles despite the harsh environment associated with mail handling machines. Moreover, there is also a need for a service station which not only caps the printhead during its periods of non-use, but which covers the cap itself and the printhead wipers when each of these components are not performing their servicing function in connection with the printhead.